The invention relates to a method for adjusting the balancing impedance of a hybrid junction for the maximization of the hybrid attenuation within a desired range of operating frequencies, preferably within a range between two operating frequencies, an upper and a lower one; the balancing impedance being formed by a first resistor and a second resistor connected in series and a capacitor connected in parallel with one of said first and second resistors.
When a four-wire connection is converted into a two-wire connection, a hybrid junction is required for the separation of the transmission directions from each other. In principle, a hybrid junction is a bridge connection which, in an optimal case, is balanced. The balancing impedance thereby equals to the line impedance. The problem lies in the choice of the balancing impedance so that it corresponds to the line impedance in each particular case as the impedance of a transmission line may vary within wide limits, depending e.g. on the cable length, the conductor diameter, the insulating material of the conductor, and the manufacturing tolerances. Consequently, a stable impedance does not even provide a passable result. Optimum balancing has been sought by connecting several different balancing impedances, which has brought some improvement in the situation. This can be done if the used line structures are known and it it is assumed that no manufacturing variation occurs. This, however, is not the case in practice but manufacturing variations may decisively alter the line impedance.
Such methods have been tried, too, in which one or more variables of the balancing impedance are adjusted. If a single variable is used, the balancing obtained is merely passable. If several variables are used, the optimum is difficult to find because the variables are dependent on each other.